1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays and other environments requiring patterning of fine structures. In a conventional lithographic apparatus, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., part of one or several dies) on a substrate (e.g., a silicon wafer, glass plate, or the like) that has a layer of radiation-sensitive material (e.g., resist). In a maskless lithography system, instead of a mask, the patterning device may include an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning”-direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
In view of the high costs of masks for use in lithographic processes and the length of time required to manufacture them, maskless lithographic systems including programmable patterning devices (e.g., spatial light modulators, contrast devices, etc.) have been developed. The programmable patterning devices are programmed (e.g., electronically or optically) to form the desired mask pattern and impart it to the beam. Types of programmable patterning means that have been proposed include micro-mirror arrays, LCD arrays, grating light valve arrays, and the like.
An example lithographic apparatus employing a programmable patterning device is found in U.S. Pat. No. 6,498,685 (the '685 patent), which is incorporated herein by reference in its entirety. In the '685 patent, a collimated illumination beam is directed onto a micro-mirror array so that the mirrors of the micro-mirror array either direct light via a beam expander onto a respective microlens in a microlens array or direct light out of the optical system. Example systems using microlens arrays to project images of masks are disclosed in U.S. Pat. No. 5,517,279 and PCT Patent Application WO 94/11781. The microlens array forms an array of small spots on a substrate and the micro-mirrors effectively act as switches to turn individual spots in the array of small spots ON and OFF. By scanning the substrate relative to the array of small spots, which is inclined to the scanning direction, as the spots are selectively activated, features corresponding to a pattern in the micro-mirror array can be built up on the substrate.
The beam expander is desirable to create a useful size imaging field because the programmable patterning device is relatively small. However, this means that the array of small spots at the substrate level is quite sparse and if the spots are small, to give a reasonable resolution, the array must be wide and inclined at only a small angle to the scanning direction in order to be able to address the whole surface of the substrate. The beam expander is complex and requires a significant amount of space. It is also a significant additional cost and additional source of errors, especially a large field lens in the beam expander. Furthermore, it reduces the optical transmission of the apparatus.
Therefore, what is needed is system and method using a lithographic projection apparatus without a beam expander that includes a programmable patterning device in which the lithographic projection apparatus can be simpler in structure than conventional devices and more compact.